1. Field of the Invention
This invention relates to the high-speed, smokeless coking of coal, and more particularly to a method of and ovens for the non-recovery coking of coal in which a sufficiently high temperature and gas retention time is provided for substantially complete combustion of the volatiles and solids released during the process to assure substantially smokeless operation of the ovens without the use of auxiliary sources of heat.
2. Description of the Prior Art
The non-recovery coking process was long used, almost exclusively, for the production of metallurgical coke. This process gradually gave way to the by-product or retort process due, at least in large part, to the value of the gas and other chemicals recovered and because the actual coking process could be conducted with less polluting emissions to the atmosphere than from the non-recovery ovens then known, and therefore the by-product process could be carried out closer to the densely populated areas which provided markets for the recovered by-products. However, in recent years, the commercial market for the recovered by-products has diminished while the cost of recovery has greatly increased with the result that the economic reasons for employing the by-product process over the non-recovery process no longer exists. This has produced a renewed interest in the non-recovery process, and substantial effort has recently been directed to increasing the efficiency of non-recovery ovens and to reducing the emissions from such ovens to acceptable limits.
One source of objectionable pollution from coke ovens, whether of the by-product or non-recovery type, has been the charging gases emitted during the charging of the oven. As coal is charged into a hot oven, a surge of gas is produced due both to the displacement of gases in the furnace by the large volume of coal and to the generation of additional gases by the vaporization of moisture in the coal and the initial burning and volatization of the newly deposited coal. This surge of gas is referred to herein as charging gas to distinguish from the gases normally evolved during the coking process. The problem of eliminating emissions during charging are discussed, for example, in U.S. Pat. Nos. 4,004,702 and 3,857,758, each of which discloses apparatus intended to solve the problem and which have, at best, been only partially effective.
A particularly troublesome form of polluting emissions from non-recovery ovens has been the unburned and partially burned solids included in the stack gases admitted to the atmosphere and which are visible as smoke. The unburned and partially burned solids have been especially high during the early stages of the coking process when the chamber is largely filled with green or uncoked coal.
Various state and local agencies charged with the protection of the environment, working with the U.S. Environmental Protection Agency, have established limits on the amount of solids which may be emitted to the atmosphere from a coking oven. For example, the Commonwealth of Virginia has established a maximum average allowable solids emission of 4.1 pounds per hour from a non-recovery type coke oven coking at a rate of one ton of coal per hour. Meeting this standard requires a very substantial reduction in solids emissions over that obtainable using the technology of the known prior art non-recovery ovens.
One prior art system for reducing the solids emission from a non-recovery oven, disclosed in U.S. Pat. No. 3,462,346, employs flues or tunnels interconnecting the coking chambers of adjacent ovens in a battery. The ovens are operated in pairs, with the ovens of each pair being on alternate cycles so that, when one oven is charged with green coal, the companion oven is approximately half through the coking cycle. In operation, the partially burned products of combustion, including solid particles, or smoke, from the green coal in one chamber is passed through the companion oven, over the hot coke bed, to facilitate burning of the solids. The combined gases pass from the hot coking chamber downwardly through downcomers in the sidewalls of the oven to sole flues beneath the hot coking chamber, then outwardly through stacks. One difficulty with this arrangement is that initial coking of the green coal is very slow due to the fact that little or no heat is supplied to the sole flues of the oven beneath the green coal bed.
Another attempt at reducing or eliminating the objectionable solids or smoke from the discharge gases of a non-recovery oven is illustrated in U.S. Pat. No. 4,045,299, which discloses the use of an ignition chamber structure including a system of checkerbricks to incinerate the partially burned distillation products discharged from the sole flues of the ovens. In order to accomplish the necessary reduction in emissions, using this prior art arrangement, it is necessary to provide an independent oil-fired burner arrangement in the ignition chamber to provide the required heat, and to supply an auxiliary draft inducing means, or fan, to draw the gases from the ignition chamber. In addition, a liquid scrubber is required for the stack.
Numerous other attempts have been made to reduce or eliminate the pollution previously thought inherent in a coking operation but, as with those discussed above, have only met with limited success. It is, therefore, a primary object of the present invention to provide an improved, high-speed, non-recovery type coking installation wherein the distillation products liberated and solid combustible materials released in a coking chamber are so completely burned before being discharged into the atmosphere as to substantially reduce the polluting emissions discharged.
It is a further object of the present invention to provide such a high-speed coking oven which is self-sustaining, requiring no auxiliary heat or fuel to complete combustion of the distillation and solid products liberated in the coking chamber.
Another object of the invention is to provide such an oven in which heat is supplied to the coking chamber through sole flues extending beneath the oven floor in which the products of distillation are burned and in which preheated combustion air is supplied to the sole flues to thereby increase the temperature in the flues.
Another object of the invention is to provide an improved high-speed smokeless non-recovery coking oven including improved means for reducing discharge of charging gases into the atmosphere during charging of the oven.